1. FIELD OF THE INVENTION
This invention relates to an ultra-violet ray curing type resin composition which is capable of being easily cured by irradiation of the ultra-violet rays, and of forming a coating film having excellent adhesive force to a base material such as metal, glass, plastic, and so forth.
2. DESCRIPTION OF THE PRIOR ART
As such ultra-violet ray curing type resin composition which has heretofore been known, there are unsaturated polyester resin, epoxy (meth)acrylate resin, urethane (meth)acrylate resin, and so forth. However, these resin compositions are not so satisfactory in their adhesive force to various base materials such as metal, glass, etc., and heat resistance of their coating films.
On the other hand, an application for patent has recently been made by General Electric Company, U.S.A. on a photo-polymerization catalyst for cationically polymerizable compounds such as epoxy resins, etc. While cured coating film of the ultra-violet ray curing type epoxy resin produced by using these catalysts is excellent in its adhesive force to the base materaial, when compared with those conventional acrylate type ultra-violet ray curing type resins, they are still inferior in the adhesive force to the base material, when compared with ordinary thermo-setting epoxy resin compositions, because the resins are cured rapidly in a unit of second by irradiation of the ultra-violet rays, which causes internal stress to remain within the coating film as cured.
In view of such circumstances as mentioned above, the present inventors strenuously repeated studies and researches with a view to obtaining an ultra-violet ray curing type resin composition which is excellent in the ultra-violet ray curing property and is capable of producing cured product having good adhesive force to the base material. As the result of such efforts made, they have found that the cured coating film of excellent ultra-violet ray curing property and having good adhesive force to the base material such as glass, metal, plastic, and so on can be obtained by use of a resin composition which consists essentially of: (A) one or more kinds of cationically polymerizable compound containing, as the principal constituent, an epoxy resin having two or more oxirane rings in one molecule thereof; (B) 0.5 to 20% by weight, with respect to the cationically polymerizable compound, of phenoxy resin having a molecular weight in a range of from 10,000 to 60,000; (C) 0.5 to 20% by weight, with respect to the cationically polymerizable compound, of polyhydric alcohol containing two or more hydroxyl group in its molecule; and (D) an effective amount of from 0.5 to 10% by weight, with respect to the cationically polymerizable compound, of a photo-initiator capable of isolating a Lewis acid catalyst which is able to initiate polymerization of the cationically polymerizable compound by irradiation of the ultra-violet rays. On the basis of this finding, they have completed the present invention.